During the last 20 years allograft heart valve transplantation in the United States has increased from about 50 to 2,000 per annum. Because of this increased demand, particularly for pediatric cases, utilization of these cryopreserved heart valves is now limited by the supply of donated human hearts. The object of this proposal is to convert xenograft heart valves into allografts in an attempt to resolve this supply problem. Low- dose-irradiate, xenograft heart valves will be treated to induce growth factor-irradiated, allogenic fibroblast ingrowth into the xenograft heart valve leaflets. Porcine heart valves and bovine fibroblasts will be used. Once the optimum source and method for fibroblast ingrowth has been determined, allogenic fibroblast-repopulated xenograft heart valve leaflets will be implanted in calves. The transplant study will be short term (3 months) and will concentrate on determining the behavior of the fibroblasts in the heart valve leaflets. The cell biology experiments will be performed at CryoLife, Inc., and the transplantation studies at Colorado State University.